The letter was also signed by Reps. Jim Costa of Fresno and John Garamendi of Walnut Grove (Sacramento County). Garamendi is a fierce protector of delta water and fisheries, which frequently puts him in conflict with San Joaquin Valley farmers over water.

The Democrats described the water cuts as “catastrophic,” saying the state proposal could “cut back all delta water pumping for agriculture and (wildlife) refuges” for the purpose of saving enough water by September to “protect public health and safety” should the drought continue next year.

They said recent rains are expected to provide “significant outflows at the delta” for the next two weeks, providing time for the state to reassess its decision.

Garamendi told us in a phone interview that the expected “zero water” allocations would “basically shut down the California water system.” He said he, the senators and Costa want the board to “consider the ramifications as well as the necessity of it.”

Garamendi said the letter appears to have had its desired effect, with the board engaging more parties to figure out how to meet minimal needs for public health and safety, agriculture, fish and industry to “work our way through this in the least damaging way possible.”

Garamendi said it was unclear what the effect of the state plan would be on the delta. “How much water would be allowed to flow for riparian purposes, unknown, maybe zero,” he said. “For fish, unknown, maybe more, maybe less, maybe none.”

Depending on how much rain falls for the rest of the dwindling season, the original plan may still have to be put in operation, Garamendi said.

“If it stops raining this week, it may very well be that nobody takes any water,” he said. Then, “we will store what can to make it through next summer and fall — and winter, maybe.”

For complete Chronicle coverage of the California drought, click here.